Porous structure and sorption properties of nitrogen-containing activated carbon

Nitrogen-containing activated carbon (NAC) derived from ammonium humates was produced and its porous structure (specific surface, pore volume) investigated. The NAC is mesoporous activated carbon with surface area of 557 m²/g and containing 2.4 wt.% of nitrogen. Sorption characteristics (sorption activity of iodine, methylene blue, benzene and metal ions Cu²⁺ and Pb²⁺) of NAC are compared with activated charcoal and BAU-A.     

Preparation of activated carbon from paper mill sludge by KOH-activation

The purpose of this study is the preparation of activated carbon using paper mill sludge collected from biological wastewater treatment plant. The char produced from pyrolysis of paper mill sludge was chemically activated with potassium hydroxide. A systematic investigation of the effect of activation agent ratio, activation temperature and time on the properties of the char was carried out in a rotary kiln reactor. The chemically activated carbons were characterized by measuring iodine and methylene blue number and specific surface area. The activated carbon prepared from char of paper mill sludge in this study had maximum iodine and methylene blue number of 726.0 mg/g and 152.0 mg/g, and specific surface area of 1,002.0 m²/g, respectively. The result of estimation on adsorption capacities of metals, the Freundlich isotherms, yields a fairly good fit to the adsorption data, indicating a monolayer adsorption of metals onto activated carbon prepared from char of paper mill sludge using a potassium hydroxide as the activating agents.     

A study of the characteristics of activated carbons produced by steam and carbon dioxide activation of waste tyre rubber

This paper presents a study into the effect of different activation conditions on the porosity and adsorption characteristics of carbon adsorbents produced from waste tyre rubber. For the purpose of this work, three carbon series were produced using different activation temperatures (between 925 and 1100 °C) and oxidising agents (steam or carbon dioxide). Carbons produced to different degrees of burn off were characterised using gas (nitrogen) and liquid phase (phenol, methylene blue and Procion Red H-E2B) adsorption. Total micropore volumes and BET surface areas increased almost linearly with the degree of activation to 0.554 ml/g and 1070 m²/g, respectively, while the development of external surface area was particularly rapid at degrees of activation above 50 wt% burn off. Steam was observed to generate a narrower but more extensive microporosity than carbon dioxide. However, carbon dioxide produced carbons of slightly larger external surface areas. Activation at higher temperatures resulted in pores of slightly larger dimensions, although this was only evident in highly activated samples. Porosity characteristics were reflected in the capacity of the carbons to adsorb species of different molecular size from solution. In this respect, steam-activated carbons presented greater capacities for the adsorption of smaller molecular size compounds (phenol), while carbon dioxide-activated carbons adsorbed larger textile dyes more effectively.     

Porous structure of crystalline polymers by exclusion effect of carbon dioxide

We investigated the morphology of high-density polyethylene (HDPE) and poly(vinylidene fluoride) (PVDF) crystallized under carbon dioxide (CO₂) by light scattering measurements and microscopic observations. The crystallization of HDPE was delayed and the ordering of the spherulite was smaller by dissolving CO₂ rather than air at ambient pressure. A fine-layered porous structure having a size of 500 nm was obtained in HDPE, while a large rod-like porous structure radiating in the spherulite was obtained in PVDF. Such a characteristic porous structure is attributed to the exclusion of CO₂ from the crystal growth front to the intercrystalline amorphous region and the growth of bubbles by the supersaturation of CO₂ in the constrained amorphous region. The exclusion effect is covered by the Keith-Padden theory through consideration of the self-diffusion in polymer-CO₂ systems; the exclusion and the growth of bubbles occur as lamellar stacks in HDPE whereas they occur as bundles of lamellar stacks in PVDF.     

Pore structure of activated carbons prepared by carbon dioxide and steam activation at different temperatures from extracted rockrose

The influence of the activation temperature on the pore structure of granular activated carbons prepared from rockrose (Cistus ladaniferus L.), extracted previously into petroleum ether, is comparatively studied. The preparation was carried out by pyrolysis of a char in nitrogen and its subsequent activation by carbon dioxide and steam (flow of water controlled to generate the same mol number per minute of water as well as carbon dioxide/nitrogen) at 700-950°C to 40% burn-off. The techniques applied to study the pore structure were: pycnometry (mercury, helium), adsorption (carbon dioxide, 298 K; nitrogen, 77 K), mercury porosimetry and scanning electron microscopy. The preparation by steam activation, especially at 700°C, yields activated carbons showing a total pore volume larger than those prepared by carbon dioxide activation. The pore structures present the greatest differences when the activations are carried out between 700 and 850°C and closer at higher temperatures. At high temperatures, the decrease of differences in pore development caused by carbon dioxide or steam is attributed to an external burn-off. The micropore structure of each activated carbon is mainly formed by wide micropores. At the lowest activation temperatures, especially at 700°C, steam develops the mesoporosity much more than carbon dioxide. At 950°C, a similar reduction of pore volume in the macropore range occurs.     

Preparation of activated carbon microspheres from phenolic-resin by supercritical water activation

Supercritical water (SCW) has been employed as an efficient activating agent for the preparation of activated carbon microspheres (P-ACS) with developed mesopores from phenolic-resin. Several processing factors that influenced the activation reaction, including activation temperature, activation duration, supercritical pressure and water flow rate were investigated. Increasing activation temperature and duration lead to larger porosity and higher specific surface area as demonstrated in the samples. Supercritical pressure change has little effect on the activation; however, there are indications that a slight increase in mesoporosity can be obtained when the pressure was raised to 36 MPa or higher. Higher water flow rate slightly enhanced the development of microporosity but had little effect on the mesoporosity. Compared with the traditional steam activation, SCW activation can produce P-ACS with more mesoporosity and higher mechanical strength.     

Capacitance properties of multi-walled carbon nanotubes modified by activation and ammoxidation

Catalytic multi-walled carbon nanotubes were modified by KOH activation at 800 °C and/or ammoxidation at 350 °C, and the effect of these treatments on the physicochemical and electrochemical properties was investigated. Whereas texture is moderately changed by ammoxidation, the chemical composition is significantly modified due to the formation of various nitrogen containing groups. The influence of nitrogenated functionality (pyridine, pyridone, NH) on charge accumulation is considered in full electrochemical capacitors, as well as in positive and negative electrodes separately, using acidic (4 mol L⁻¹ H₂SO₄) and alkaline (7 mol L⁻¹ KOH) electrolytes. The presence of nitrogen in the carbon network, especially in the form of pyridone/pyrrolic (N5) and/or pyridine (N6) groups, affects the electron density and enhances the charge affinity of the carbon material. It seems that the nitrogen groups improve particularly the capacitance performance of the negative electrode operating in alkaline medium. Besides the nitrogenated groups, the oxygenated functionality plays also an important role for the ammoxidized nanotubes. Generally, a few-fold increase of capacitance was observed in the N-enriched carbon nanotubular samples. Apart of this capacitance improvement, the presence of nitrogen in the carbon network limits significantly the leakage current and diminishes the self-discharge of supercapacitors.     

化学活化法制备活性炭的正交试验分析

采用正交试验分析法对化学活化法制备木质活性炭的工艺过程进行设计,选择浸溃比,活化温度和活化时间3个因素,3个水平的正交试验方法进行了相关的实验：实验结果炙明,磷酸活化法制备木质活性炭工艺过程中,对活性炭得率影响最大的因素是浸渍比和活化温度,对活性炭亚甲蓝吸附值影响最大的因素是浸溃比,对活性炭苯酚吸附值影响最大的因素是活化时间。综合制备木质活性炭的得率和吸附性能影响因素．浸渍比是化学活化法制备木质活性炭的最重要的影响因素。     

Porous carbon materials produced by the chemical activation of birch wood

It was established that the main factors responsible for the yield and specific surface area of porous carbon materials obtained by the chemical activation of the wood of birch are the nature of a modifying agent and the temperature of pyrolysis. The additional opening of the porous structure of the product of the chemical activation of wood occurs at the stage of its water treatment as a result of the removal of water-soluble compounds. The conditions of the carbonization of birch wood modified with H₃PO₄, KOH, and ZnCl₂ were chosen in order to provide the significant development of the porous structure of carbon materials. The porous carbon material with the highest specific surface area (more than 2560 m²/g) was obtained by the water washing of the product of the carbonization of birch wood modified H₃PO₄ at 400°C.     

Preparation of activated carbons from olive-tree wood revisited. II. Physical activation with air

Olive-tree has been grown in the Mediterranean countries for centuries. For an adequate development of the tree it must be subjected to different treatments such as trimming, large amounts of a woody residue being produced. Such a residue has been traditionally used as a domestic fuel or simply burnt in the landfield. In both cases greenhouse gases are generated to a large extent. Thus, the preparation of activated carbons from olive-tree wood appears as an attractive alternative to valorize this by-product. Commonly, two activation strategies are used with such an aim, namely chemical and physical activation. In this study, the optimization of the physical activation method with air for the production of activated carbon has been analyzed. The results obtained clearly show that if the preparation conditions are adequately controlled, it is possible to prepare activated carbons showing tailored properties in terms of micro- or mesoporous texture and surface area.     

Preparation and adsorptive properties of cellulose-based activated carbon tows from cellulose filaments

A series of cellulose-based activated carbon tows were prepared in a vertical tube furnace in the presence of reactive mixed gases after pretreatment with complex inorganic flame-retarding reagents under different burn temperatures and delivery speeds. The cross and vertical sectional surface states of activated carbon tows were observed with a SEM instrument. The surface characteristic, BET surface area, pore volume and pore radius of activated carbon tows were measured with N₂ at 77 K with a Quantachrome Autosorb-6 Sorption System. The adsorptive properties of gases and organic solvents on activated carbon tows (ACT) and granular activated carbon (GAC) were also determined.     

Preparation and characterization of mesoporous activated carbon from waste tires

Activated carbons were produced from waste tires and their characteristics were investigated. Rubber separated from waste tires was first carbonized at 500 °C in N₂ atmosphere. Next, the obtained chars were activated with steam at 850 °C. As a result, fairly mesoporous activated carbons with mesopore volumes and BET surface areas up to 1.09 cm³/g and 737 m²/g, respectively, were obtained. To further improve the porous properties of the activated carbons, the char was treated with 1 M HCl at room temperature for 1 day prior to steam activation. This treatment increased mesopore volumes and BET surface areas of the activated carbons up to 1.62 cm³/g and 1119 m²/g, respectively. Furthermore, adsorption characteristics of phenol and a dye, Black 5, on the activated carbon prepared via acid treatment were compared with those of a commercial activated carbon in the liquid phase. Although the prepared carbon had a larger micropore volume than the commercial carbon, it showed a slightly lower phenol adsorption capacity. On the other hand, the prepared carbon showed an obviously larger dye adsorption capacity than the commercial carbon, because of its larger mesopore volume.     

Flue gas desulphurization by activated carbon fibers obtained from polyacrylonitrile by-product

By pyrolysis of a polyacrylonitrile textile by-product, subsequent activation by CO₂ and treatment (at high temperature) with a N₂ flow containing a low percentage of O₂ or of NH₃, three carbonaceous matrices are obtained having a high surface area and surface sites with basic characteristics. The SO₂ sorption properties of these carbon samples (in the temperature range between 100 and 160 °C) from gaseous mixtures having a similar composition to flue gases, seems to be promoted by nitrogen bonded to carbon. The SO₂ adsorbed by the carbons can be divided, by suitable extraction with distilled water, into: (i) desorbable, such as SO₂ or H₂SO₃, (ii) desorbable, such as SO₃ or H₂SO₄, (iii) non-desorbable. Following 10 SO₂ adsorption and desorption cycles, the surface area values of the activated carbons remain practically constant, while both the content of the acidic surface sites and the amount of non-desorbable SO₂ increase; this results in the decrease in the SO₂ carbon sorption property seeming to be even more marked for the carbon sample containing nitrogen.     

Preparation and electrochemical properties of pitch-based activated carbon aerogels

The porous structure of pitch-based carbon aerogels (P-CAs) can be modified by KOH activation. It is found that decreasing the carbonization temperature of precursor CAs and increasing the mass ratio of KOH to CAs help to the formation of 0.7 nm-sized micropores and 2.7 nm-sized mesopores, respectively. The origin and the pore size of micropores play an important role in controlling electrochemical properties. The carbonization-forming micropores have stronger energy storage efficiency than activation-forming micropores, and only those with diameter below 1 nm (Microp < 1 nm) are the crucial place to storage energy. Due to the substantive increase of the number of the Microp < 1 nm, the highest specific capacitance of the as-prepared activated samples can reach 187.2 F g⁻¹ at 5 mA cm⁻², 1.8 times as large as that of their precursor CAs. Furthermore, this capacitance is still up to 173.3 F g⁻¹ when increasing the current density to 50 mA cm⁻², indicating that the activated samples have a high-rate charge–discharge performance.     

Production of activated carbon from olive bagasse by physical activation

Activated carbons were produced from olive bagasse and their characteristics were investigated. Olive bagasse was first carbonized at 500 °C in N₂ atmosphere. Then, the obtained chars were activated with steam. The effects of activation temperature and duration were examined. The resultant activated carbons were characterized by measuring their porosities and pore size distributions. The activated carbons produced had the BET surface areas ranging from 523 to 1106 m²/g. The total pore volume was increased from 0.2981 to 0.6067 cm³/g. Adsorption capacity was demonstrated by the iodine numbers. The surface chemical characteristics of activated carbons were determined by FTIR spectroscopic method and Boehm's titration method. The microstructure of the activated carbons prepared was examined by scanning electron microscopy (SEM). The experimental data was proved that the properties of activated carbons depend on the final temperature of the process and duration of treatment at the final temperature.     

Application of physical vapor deposition process to modify activated carbon fibers for ozone reduction

This study utilized the activated carbon fiber (ACF) modified with metal catalyst via physical vapor deposition (PVD) process (ACF/PVD) to diminish ozone. Furthermore, the ozone removal efficiency of ACF/PVD was compared with that of original ACF and ACF modified with metal catalyst via impregnation process (ACF/impregnation). In addition to the kinds of coated metal and the inlet ozone concentrations, the effects of the coating thickness and the reaction temperature on ACF/PVD for ozone removal were also examined. The results indicate that the ozone removal efficiency of ACF/PVD is better than that of original ACF and ACF/impregnation. The ozone removal efficiency of different metal-coated ACF/PVD in the superior order is gold (Au), and manganese (Mn). The increase of Au-coated thickness (3 nm to 80 nm) on ACF/PVD will enhance the ozone removal. However, when the Mn-coated thickness on ACF/PVD is larger than 15 nm, the ozone removal efficiency displays a declining trend. Furthermore, a higher reaction temperature will result in a better ozone removal of ACF/PVD and the original ACF.     

Destruction of methyl ethyl ketone vapor by ozone on activated carbon

This study attempts to combine the technologies of adsorption of volatile organic compounds (VOCs) on activated carbon and the oxidation of the VOCs by ozone (O₃). In the adsorption/oxidation process, the effects of ozone on the adsorption characteristics of methyl ethyl ketone (MEK) vapor on activated carbon are investigated. The kinetic parameters of the reaction for MEK vapor and O₃ on activated carbon are also determined. The results show that the destructive efficiencies of MEK by 1000 ppmv O₃ on activated carbon are from 12.4% to 48.5%. From the power law kinetic model, the apparent kinetic constant, k, is obtained with a value of 0.0438 h⁻¹. Moreover, from the analytical results of the Arrhenius equation, the activation energy, E_a, is found to be 5.12 kcal/mol and the value of rate constant, A, is 189.54 h⁻¹. From the Langmuir–Hishelwood model [Escobar, P., Beroy, Q., Iritia, P.P., Huerta, J.H., 2004. Kinetic Study of the Combustion of Methyl–Ethyl–Ketone over α-Hematite Catalyst. Chem. Eng. J. 102, 107] the values of the kinetics parameters k^′LH${k^{\prime }}_{\text{LH}}$ and k_LH were 0.035 and 0.6183, respectively. Finally, the modified Wheeler equation [Busmundrud, O., 1993. Vapour Breakthrough in Activated Carbon Beds. Carbon 31, 279; Wood, G., Moyer, E.S., 1989. A Review of the Wheeler Equations and Comparison of Its Applications to Organic Vapor Respirator Cartridges Breakthrough Data. Am. Ind. Hyg. Assoc. J. 50, 400; Yoon, Y.H., Nelson, J.J., 1984. Application of Gas Adsorption Kineties I. A Theoretical for Respirator Cartridge Service Life. Am. Ind. Hyg. Assoc. J. 45, 509] in combination with the power law kinetic model or Langmuir–Hishelwood is used to predict the breakthrough curves. The destruction of MEK can be effectively promoted as the bed height of activated carbon and the concentration of ozone increase. When the ozone concentration is increased to 7800 ppmv and the amount of activated carbon is increased to 5 g the destructive efficiency of MEK is still greater than 95% even after a prolonged operational time. From the results of this study, an adsorption process in combination with ozone oxidation shows potential for the control of VOCs and odor.